Wireless Display Systems and Stylii

1. A stylus comprising: a stylus tip; a first ultrasonic transmitter controllable by application of pressure to the stylus tip; a second ultrasonic transmitter; a first switch to control the second ultrasonic transmitter; and a higher frequency transmitter to provide a time reference for the first and second ultrasonic transmitters; wherein the stylus is to use with a wireless display system having a projection plane and at least three ultrasonic receivers, wherein the first ultrasonic transmitter is to transmit ultrasonic energy to at least two of the ultrasonic receivers in determining a position of the stylus relative to the projection plane in two dimensions, and wherein the second ultrasonic transmitter is to transmit ultrasonic energy to at least three ultrasonic receivers in determining a position of the stylus relative to the projection plane in three dimensions.

2. The stylus of claim 1 wherein the first and second ultrasonic transmitters are to emit ultrasonic energy at different frequencies.

3. The stylus of claim 2 wherein the first and second ultrasonic transmitters are to emit ultrasonic energy between substantially forty kilohertz and eighty kilohertz.

4. The stylus of claim 1 wherein the first and second ultrasonic transmitters are to emit ultrasonic energy at the same frequency.

5. The stylus of claim 1 further comprising a pressure-activated switch coupled to the stylus tip, wherein the pressure-activated switch is operable to turn on the first ultrasonic transmitter when pressure is applied to the stylus tip.

6. The stylus of claim 5 further comprising a higher frequency transmitter to provide a time reference for the first and second ultrasonic transmitters, wherein the higher frequency transmitter is controllable by one of the first switch and the pressure-activated switch.

7. The stylus of claim 1 wherein the first ultrasonic transmitter is located at the stylus tip, and wherein the first ultrasonic transmitter comprises a polymer.

8. The stylus of claim 1 wherein the first ultrasonic transmitter is located at the stylus tip, wherein the first ultrasonic transmitter is cylindrical and formed of a polymer material, and wherein the first ultrasonic transmitter is to transmit onmi-directional ultrasonic energy.

9. The stylus of claim 1 wherein the second ultrasonic transmitter is located at an end of the stylus opposite the tip, and wherein the second ultrasonic transmitter comprises a piezoelectric material.

10. The stylus of claim 1 wherein the second ultrasonic transmitter is located at an end of the stylus opposite the tip, and wherein the second ultrasonic transmitter comprises a plurality of semi-hemispherical discs of piezoelectric material.

11. The stylus of claim 1 wherein the higher frequency transmitter comprises one of a radio frequency transmitter and an infrared transmitter.

12. The stylus of claim 1 wherein the first and second ultrasonic transmitters and the higher frequency transmitter are burst transmitters.

13. The stylus of claim 12 wherein the first and second ultrasonic transmitters are to transmit bursts between 50 and 100 pulses/second.

14. The stylus of claim 1 , wherein at least one of the ultrasonic receivers includes a higher frequency receiver, and wherein the higher frequency transmitter is to transmit one of radio frequency energy and infrared energy to the higher frequency receiver.

15. A wireless display system comprising: at least three ultrasonic receivers mountable at different locations on a projection surface; a stylus comprising a first ultrasonic transmitter to transmit ultrasonic energy to the ultrasonic receivers, a second ultrasonic transmitter to transmit ultrasonic energy to the receivers, wherein the first and second ultrasonic transmitters are to transmit ultrasonic energy at different frequencies, wherein two-dimensional position coordinates of the stylus are to be determined when ultrasonic energy is received by the receivers at a first frequency, and wherein three-dimensional position coordinates of the stylus are to be determined when ultrasonic energy is received by the receivers at a second frequency; and a computer coupled to the ultrasonic receivers, wherein the computer is to determine the two-dimensional and three-dimensional position coordinates of the stylus relative to the projection surface.

16. The wireless display system of claim 15 wherein the first ultrasonic transmitter is controllable by a user-operable switch on the stylus.

17. The wireless display system of claim 15 wherein the first ultrasonic transmitter is located at an end of the stylus opposite a tip of the stylus, and wherein the first ultrasonic transmitter comprises a plurality of semi-hemispherical discs of piezoelectric material.

18. The wireless display system of claim 15 wherein at least one of the ultrasonic receivers is to calculate time of arrival information.

19. The wireless display system of claim 15 wherein the computer is coupled to the ultrasonic receivers via a wireless interface.

20. The wireless display system of claim 19 wherein the wireless interface comprises a processor to calculate time of arrival difference information.

21. The wireless display system of claim 15 further comprising a projection system responsive to the computer to project an image onto the projection surface.

22. The wireless display system of claim 15 wherein the stylus further comprises a second ultrasonic transmitter to transmit ultrasonic energy to the ultrasonic receivers, wherein the first and second ultrasonic transmitters are to transmit ultrasonic energy at the same frequency.

23. The wireless display system of claim 15 and further comprising a higher frequency receiver co-located with one of the ultrasonic receivers, and wherein the stylus further comprises a higher frequency transmitter to provide a time reference for the ultrasonic receivers.